JP 2012-231562A discloses an example of a DC/DC converter that can perform a protection operation when an overcurrent anomaly occurs. The DC/DC converter disclosed in JP 2012-231562A is provided with a shunt resistor between a switching element of a voltage conversion unit (step-up unit) and ground, and forms a configuration that compares a mid-point voltage between the switching element and the shunt resistor with a reference voltage (second threshold voltage) using a comparison unit (third comparison unit). The reference voltage (second threshold voltage) is generated by a voltage generation unit (second voltage generation unit) with reference to ground, and when the mid-point voltage between the switching element and the shunt resistor becomes higher than the reference voltage, the output signal of the comparison unit (third comparison unit) switches to high level, and the switching element turns off.
The DC/DC converter disclosed in JP 2012-231562A forms a circuit configuration that determines whether the current flowing through the shunt resistor provided on the ground side exceeds a threshold value by comparing the potential at one end of the shunt resistor with a reference potential that is generated by the voltage generation unit. However, with this circuit, there is a risk of not being able to perform the determination accurately if the ground potential varies.
For example, in the case where circuitry of the power system in which the shunt resistor is provided is connected to ground (power ground) of the electric power system, the potential (detection potential) at one end of the shunt resistor will be generated with reference to power ground. On the other hand, in the case where the voltage generation unit for generating the reference potential is connected to ground (signal ground) of the signal system, the reference potential will be generated with reference to signal ground. With this circuit, a condition for accurately determining whether the current flowing through the shunt resistor exceeds the threshold value is that the potential difference between power ground and signal ground is zero or very small, and accurate determination is difficult when one or both grounds vary. In particular, since a high current flows to and from power ground, there is concern about the tendency of the ground potential to vary depending on the ground configuration and the state of the inflow/outflow current, and the tendency for a difference to arise with the potential of signal ground. Note that the problem of the accuracy of current determination dropping due to variation in the ground potential is not limited to a configuration in which power ground and signal ground are separated, and is cause for concern if the connection position of the shunt resistor is separated from the connection position of the voltage generation unit that generates the reference potential.
The present description has been made in order to solve at least one of the abovementioned problems, and an object thereof is to more accurately determine whether a current flowing between a voltage conversion unit and a reference conduction path is in a predetermined overcurrent state.